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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

462

SOAPS

and olive, arachis,' sesame, cottonseed and coco-nut oils ; yellow soaps
may contain resin and palm oil, and green or brown ones, sulphocarboh
oil and resin. Further, the solidifying point, acid and iodine numbers
and certain colour reactions and other investigations of the fatty acids
obtained from a soap give information, up to a certain point, of the char-
acter of the fats used.

For example : Soaps prepared from oleine give fatty acids which solidify
at a low temperature and contain only small quantities of solid acids (for
examination of these, see p. 384).

Soaps from coco-nut oil give fatty acids with an acid number above 205
and a low iodine number.

Those from linseed and other drying oils contain hydroxy-acids insoluble
in the cold in petroleum ether and yield fatty acids with a high iodine
number.

Soaps from cottonseed, sesame and arachis oils give fatty acids which
show .Milliau's and Villaveccllia and Fabris' reactions and contain arachidic
acid (see Cottonseed, Sesame and Arachis Oils, preceding chapter).

Resin soaps give the reaction for resin with acetic anhydride and sul-
phuric acid (see 9).

Tests for cholesterol and phytosterol (see Hog's Fat) show whether a
soap contains animal or vegetable fats.

12. Extraneous Substances.—These may be of varied character
and principally as follows :

(a] MINERAL SUBSTANCES. Alkaline chlorides, sulphates, carbonates
and phosphates, water glass, borax, heavy spar, kaolin, talc, siliceous sand,
pumice, tiipoli, etc. Some soaps (especially powdered) contain also oxidising
agents, such as sodium peroxide, perborates, percarbonates and persulphates.

All these substances may be recognised and determined by treating
the soap with absolute alcohol and examining the insoluble residue by the
ordinary analytical methods, both qualitative and quantitative.

(6) VARIOUS ORGANIC SUBSTANCES. These may consist of starch, flour,
dextrin, sugars (saccharose, glucose, molasses), vegetable gum, albumin
and casein. Such substances also remain undissolved when the soap is
treated with absolute alcohol and may be detected in the residue by means
of the microscope, by treating with iodine (starch, dextrin), by the rotatory
and reducing powers (sugars), by the, way in which they burn (proteins,
etc.).

(c)  ALCOHOL.   About 50 grams of the soap are dissolved in 100 c.c. of
tepid water and decomposed with a slight excess of dilute sulphuric acid
and filtered.   The filtrate (which should not be much more than 150 c.c.) is
neutralised with potash and distilled, 100 c.c. of distillate being collected.
From the density of this the alcohol is calculated.

(d)   PERFUMES.   These consist of various essential oils or of nitrobenzene
(mirbane oil).   To detect them, 30-50 grams of the. soap are dissolved in
a little water, decomposed with a slight excess of dilute sulphuric acid and
distilled in a current of steam, the distillate, being collected in a very narrow
cylinder,

The volatile oil collects in drops or in a thin layer at the surface of the foot-note.mately N/40 solution) and the titer,